Heat-sensitive copy-sheet



April 14, 1964 w. R. woRKMAN '3,129,101

HEAT-SENSITIVE COPY-SHEET Filed Nov. 1. 1961 United States Patent Oiice 3,129,101 Patented Apr. 14 1964 This invention relates to heat-sensitive copy-sheet products useful in thermographic copying processes and capable of providing fully stabilized permanent copies of graphic originals, and to methods of making and using the same.

One well-known and commercially important method for copying typewritten oice correspondence and other differentially radiation-absorptive graphic originals employs a thermographic copying procedure involving brief irradiation of the original with high-intensity radiation, such as infra-red radiation, while in heat-conductive pressure-contact with the heat-sensitive copy-sheet. Image areas of the copy-sheet corresponding to the radiationabsorptive inked areas of the original are visibly changed; background areas remain unchanged and still heat-sensitive. The present invention provides for the preparation, on initially heat-sensitive copy-sheets, of thermographic copies having visibly distinct image areas but in which the background areas are stabilized, i.e., rendered insensitive to heat. Stability is attained` without chemical treatment, as with solutions or vapors, simply by subjecting the initially formed copy to additional radiation. The process may alternatively be applied in reverse, background areas being rst insensitized and image-forming areas subsequently visibly changed; or the two steps may be accomplished in a single operation.

The process is illustrated schematically in the accompanying drawing, in which the composite of copy-sheet and graphic original is shown iirst irradiated with intense infra-red radiation to form a heat-induced image, and then exposed to ultraviolet radiation to deactivate the surrounding background areas.

One form of heat-sensitive copy-sheet which has previously been found useful in thermographic copying comprises a visibly heat-sensitive layer containing dye-forming reactant materials which when heated together, as in the thermographic reproduction process just described, form an azo dye by a reaction involving oxidative coupling. Typically, a mixture of a heterocyclic hydrazone, an azo coupler, and, as an oxidizing agent, an organic amide having a positive halogen atom attached to a nitrogen atom, is deposited with a small amount of a suitable film-forming binder on a paper, film, or other thin flexible carrier web. The sheet is stable at room temperature, but localized heating of image areas, eg., in the thermographic copying process or by brief contact with heated metal surfaces at temperatures of the order of 9\0-l50 C., causes rapidreaction and color formation. The unheated background areas may subsequently be similarly visibly changed by heating.

It has now been found that heat-sensitive copy-sheets as just described may be made capable of desensitization by actinic radiation, by selecting as the halogen-containing organic amide oxidizing agent a normally solid photosensitive N-halo-sulfonanilide, preferably an N-chlorosulfonanilide wherein a positive chlorine atom is attached to a nitrogen atom which in turn is attached to a carbon atom of an aromatic ring.

Exemplary of the photosensitive N-halo-sulfonanilides useful in the practice of Athe invention are the followmg:

N-chlorobenzenesulfonanilide; N-chloro-p-toluenesulfonanilide;

N-chloro-m-nitrobenzenesulfonanilide; N-chloro-N-(m-toluene benzenesulfonamide; N-chloro-N-(m-chlorophenyl)benzenesulfonamide; N-chloro-m-chlorobenzenesulfonanilide; N-chloro-Z-diazo-l-naphthol-S-sulfonanilide; and N,N'-dichloro-biphenyl-4,4-disulfonanilide.

As noted hereinabove, an essential component of copysheets according to the present invention is a heterocyclic hydrazone. In order to provide stability and to avoid premature color formation in the heat-sensitive copy-sheet during storage prior to use, the hydrazone component is introduced in the form of a normally solid condensation composite of a heterocyclic hydrazone and an aminereactive organic compound. Typical of such condensation products are the following:

3-methyl-Z-benzothiazolinone tetradecanoylhydrazone; 3-methy1-x sulfo 2 benzothiazolinone acetylhydrazone (wherein the x signies that the specific position of the sulfo group on the benzene ring is uncertain); 3-methyl-2-benzoselenazolinone acetylhydrazone; 3-ethyl-Z-benzoxazolinone benzenesulfonylhydrazone; l,3dimethyl-S-methoXy-Z-benzimidazolinone benzoylhydrazone; 3-methyl-4,5,6,7-tetrahydro-2-benzothiazolinone acetylhydrazone; l-methylcarbostyril phenoxyacetylhydrazone; Z-methylisocarbostyril acetylhydrazone; 3,3-dimethyl-l-ethyloxindole octanoylhydrazone; l-methylnaphtho( 1,2-d thiazolin-Z-one acetylhydrazone, 3-methyl-Z-benzothiazolinone methanesulfonylhydrazone; 3-methyl-Z-benzothiazolinone acetylhydrazone; 3-methyl-Z-benzothiazolinone semicarbazone; 3-methyl-Z-benzothiazolinone` p-toluenesulfonylhydrazone;

and 3-methyl-Z-benzothiazolinone carbethoxyhydrazone.

The hydrazone condensation composites and the photosensitive l\lhalosulfonanilides are capable of reacting togather under the conditions obtained in thermographic reproduction processes, with oxidation of the former to intermediate diazonium compounds or residues which are reactive with azo coupling components to yield azo dyes.4

Phenol, naphthol, aromatic amine, and alpha-keto methylene azo coupler components are all useful, although the naphthol-based Naphtol AS series of azo couplers are preferred. Representative examples of azo coupler components which have been found particularly useful in the copy-sheets of this invention are:

v 2-hydroxy-3-naphthanilide;

Certain hydrazone-coupler composites which combine the functions of the oxidizable diazonium-forming hy drazone and .the diazonium-reactive dye-forming azo coupler component may be used together with or in place of such coupler component or of the mixture of separate coupler and hydrazone, with theadded advantage of generally darker-colored heat-reaction products thangwould normally be anticipated on the basis of reaction between the diazonium and coupler fragments forming such composites. One such composite is 3-methyl-2-benzothiazolnone-l'-hydroxy-2'-naphthoylhydrazone, melting at 194 C. and prepared by heating under vacuum, with elimination of phenol, a mixture of approximately equimolar quantities of 3-methyl-2-benzothiazolinone hydrazone and phenyl-1-hydroxy-2-naphthoate Other composites, prepared by analogous condensation reactions and useful in the practice of the invention, include:

3-methyl-Z-benzothiazolinone 2-hydroxy-3naphthoyl hydrazone;

3-methyl-2-benzothiazolinone l-phenyl-5-pyrazolone3- carbonylhydrazone;

3-methyl-2-benzothiazolinone benzoylacethydrazone;

3-methyl-Z-benzothiazolinone 2naphthol7'-sulfonylhydrazone;

3-methyl-Z-benzothiazolinone salicylylhydrazone; and

3-methyl-4,5,6,7-tetrahydrobenzothiazolinone l-hydroxy- 2-naphthoylhydrazone.

Stoichiometric proportions of the several reactants may be determined and are effective but do not necessarily produce the best results. The color-forming components must be present in amounts sufficient to produce a readily visible change in the copy-sheet on heating, but may be considerably diluted with non-reactive components, e.g., resins, polymeric binder materials, pigments or fillers, or various other additives. For example, addition to the heat-sensitive layer of significant amounts of titanium dioxide pigment provides a white background against which the heat-formed colored image areas show increased contrast.

Sufficient of the N-halo-sulfonamide oxidizing agent must be present to permit adequate oxidation of hydrazone to reactive diazonium intermediate at heated image areas so that an effectively visible image is produced; but excess amounts provide no useful function and in fact reduce the rate at which desensitization of background areas may be accomplished.

All of the reactants may be mixed together in a common binder composition and applied as a single layer to a paper or other paper-like permanent carrier web, or coated on a temporary support and then removed in dry form as a self-sustaining film, or distributed between separate paper-like carriers which are temporarily held in face-to-face contact as a unitary heat-sensitive copysheet product. Preferably, the N-halo-sulfonamide component is applied as a separate coating over a previously applied and dried layer of a mixture of hydrazone condensation composite and azo coupler component on a paper or film support web, the reactants in each case being dissolved or dispersed in suitable solutions of resinous or polymeric film-forming binders. Where the heatsensitive layer is thus formed by multiple applications, binders and solvents are ordinarily selected so that subsequently applied coatings will not dissolve the previously applied and dried coating. Either or both of the hydrazone condensation composite and the azo coupler component may be either dissolved or intimately dispersed in the coating composition, depending on the particular solvent or solvent mixture required for the polymeric binder. Although the same is generally true of the oxidizing agent also, it has been found preferable to select binders and solvents such that the oxidizing agent is applied in solution form, since when thus prepared the resulting copy-sheet is found to be more readily desensitized on exposure to actinic radiation. Where a reactant is insoluble in the binder solution, effective dispersion is conveniently obtained by prolonged mixing in a ball mill; the same technique has also been used with the soluble materials.

The following examples will serve to illustrate but not to limit the invention.

Example 1 N-chlorobenzenesulfonanilide is first prepared by adding cold hypochlorous acid solution to a pre-cooled solution of 23.3 grams of benzenesulfonanilide in 1,00 ml. of chloroform. The hypochlorous acid is prepared from 25 g. of potassium bicarbonate and g. of cold 18% sodium hypochlorite solution and is added to the chloroform solution in two equal and separate portions with strong agitation. The resulting N-chlorobenzenesulfonanilide is recovered by evaporation after drying. After recrystallization from chloroform-heptane mixture, the product melts at 56-56.5 C.

A mixture of 2.68 grams of the N-chlorobenzenesulfonanilide in 100 g. of a 10% solution of Parapol S-50 styrene-butadiene polymer in heptane is prepared by ball milling. In another 100 g. portion of the binder solution there is similarly mixed 3.49 g. of B-methyI-Z-benziothiazolinone-1'-hydroxy-2naphthoylhydrazone. Equal parts by Weight of the two mixtures are blended together and coated on map overlay tracing paper by means of a coating bar, using a 2-mil (0.002-inch) orifice, and the solvent removed by evaporation at room temperature.

The resulting sheet is an off-white in appearance. It converts to a dark purple on brief contact with a heated metal test bar at about C. It produces effective copy of printed or other graphic originals in the thermographic copying process, in the form of dark purple image areas and unchanged off-white background areas. Th-embackground areas remain heat-sensitive, but are effectively desensitized by exposure for 30 seconds to ultraviolet light as obtained from a B-H6 high pressure mercury arc lamp at a distance of 8 inches. The colored image areas are not visibly affected by exposure to the ultraviolet light.

Example 2 A. A solution of 0.268 gram of N-chlorobenzenesulfonanilide and 1.0 gram of ethyl cellulose in 9.0 g. of acetone is first coated on oriented Mylar polyester film at an orifice of 3 mils, and dried at room temperature. A second coating is then applied, also at an orifice of 3 mils, using the hydrazone-Parapol-heptane dispersion of Example l. The dried sheet produces an intense purple image in the thermographic copying process; the background areas are desensitized by exposure of the sensitive layer through the Mylar film to radiation from the B-H ultraviolet lamp for 3 minutes at a distance of 8 inches.

B. In an alternative structure the second coating is applied directly to heavy white paper and dried, to produce an image sheet which, in conjunction with the first coating on the polyester film, constitutes a heat-sensitive copysheet product having additional uses. As an example, the coated polyester film is first exposed through a positive transparency, such as indicia printed in opaque ink on a transparent film backing, to light from a B-H6 lamp at 8 inches for three minutes. The film is then placed in face-to-face contact with the coated paper, the composite is heated at 120 C. for a few seconds, and the film removed. A purple image appears on the coated paper in areas corresponding to the inked image areas of the original.

Example 3 2-diazo-l-naphthol-S-sulfonyl chloride, 2.68 g., and aniline, 1.86 g., are reacted together in benzene at room temperature, yielding 2.4 g. of Z-diazo-l-naphthol-S-sulfonanilide melting at -140.5141.5 C. This compound is then converted, by reaction with cold hypochlorous acid, to the N-chloro compound, M. 5070 C.

Map overlay tracing paper is first coated with a 2-mil layer of a mixture of 3.49 g. of 3-methyl-2-benzothiazolinone-l-hydroxy-2naphthoylhydrazone in 100 g. of 1.0% Parapol S-50 in heptane, and the coating is dried. A further layer is then applied of 2 mils of a mixture of 0.36 g. of the N-chloro-2-diazo-l-naphthol-S-sulfonanilide, 1 g. of Parapol S-50, 1 g. of acetone, and 9 g. of heptane. The dried product is useful as a light-desensitizable heatsensitive copy-paper, producing effective copy in the thermographic copying procedure in the form of purple image areas on an olf-white background which is desensitized by exposure to radiation from the B-H6 lamp for 30 seconds at 8 inches.

Example 4 Approximately equal weights of N-chloro-Z-diazo-lnaphthol-S-sulfonanilide and 3-methyl-2-benzothiazolinone-1hydroxy2naphthoyl hydrazone are dissolved together in benzene. The solution is applied to moderately absorbent paper and the sheet dried in an air blast at room temperature. The sheet is rst exposed to a lightimage from a General Electric VA-20B ultraviolet lamp at a distance of about 2 inches and for about 3Q seconds, through a photographic negative transparency in contact with the sheet. It is then briey heated by uniform contact with a heated metal surface. The light-struck areas remain visibly unchanged; the protected areas are immediately converted to a deep purple color.

Hydrazone-coupler condensation composites such as the 3-methyl-Z-benzothiazolinone-l'hydr0xy 2 naphthoyihydrazone of the examples provide both the diazon1um and the coupler functions required in the visibly heatsensitive layer. The color of the colored image areas obtained with these materials is significantly different, in most cases being much darker, than the color which might be anticipated on the basis of the diazonium and coupler moieties presumably liberated on oxidation of the composite. The material is convenient to use, and ordinarily will be preferred in these copy-paper constructions. However it will be understood that condensation composites of heterocyclic hydrazones with various aminereactive compounds other than azo coupler components, such for example as various carboxylic acids, organic sulfonic acids, cyanates, isothiocyanates arid aldehydes, when employed in conjunction with appropriate 'azo coupler components, likewise undergo a color-forming reaction when heated together with an N-chlorosulfonauilide photosensitive oxidizing agent in the practice of this 1nvention.

What is claimed is as follows:

l. A heat-sensitive copy-sheet product useful in the thermographic reproduction of diierentially radiationabsorptive graphic originals and capable of providing permanent reproductions stable against further heating, said copy-sheet product including a visibly heat-sensitive layer containing, in intimate association, a normally solid condensation composite of a heterocyclic hydrazone and an amine-reactive organic compound, and a photosensitive N-halo-sulfonanilide oxidizing agent solid at temperatures below about C. and which is rendered inactive as an oxidizing agent by exposure to actinic radiation; and said layer including an azo coupler component.

2. A heat-sensitive copy-sheet useful in the thermographic reproduction of differentially radiation-absorptive graphic originals and capable of providing permanent reproductions stable against further heating, said copysheet including a visibly heat-sensitive layer containing, in intimate association, a normally solid condensation cornposite of a heterocyclic hydrazone and an amine-reactive organic compound, a normally solid azo coupler component, and a photosensitive N-chloro-sulfonanilide oxidizing agent solid at temperatures below about 55 C. and which is rendered inactive as an oxidizing agent by exposure to ultraviolet radiation.

3. A heat-sensitive copy-sheet useful in the thermographic reproduction of differentially radiation-absorptive graphic originals and capable of providing permanent reproductions stable against further heating, said copysheet including a visibly heat-sensitive layer containing, in intimate association, a normally solid condensation composite of a heterocyclic hydrazone and an amine-reactive azo coupler component, and a photosensitive N- chloro-sulfonanilide oxidizing agent solid at temperatures below about 55 C. and which is rendered inactive as an oxidizing agent by exposure to ultraviolet radiation.

4. A heat-sensitive copy-sheet product useful in the thermographic reproduction of differentially radiationabsorptive graphic originals and capable of providing permanent reproductions stable against further heating, said copy-sheet product including a visibly heat-sensitive layer containing, in intimate association, a normally solid condensation composite of a heterocyclic hydrazone and an amine-reactive organic compound, and an N-haloarylsulfonanilide in which the aromatic nucleus contains at least one hydrogen atom in an active position to the anilide group, said N-haloarylsulfonanilide being rendered inactive as an oxidizing agent by exposure to actinic radiation; and said layer including an azo coupler component.

References Cited in the le of this patent UNITED STATES PATENTS 2,593,911 Neumann et al. Apr. 22, il952 2,807,544 Frederick Sept. 24, 1957 2,967,784 Newman et al. a Jan. 10, 1961 2,995,465 Richey Aug. 8, 1961 2,995,466 Sorensen Aug. 8, 1961 

1. A HEAT-SENSITIVE COPY-SHEET PRODUCT USEFUL IN THE THERMOGRAPHIC REPRODUCTION OF DIFFERENTIALLY RADIATIONABSORPTIVE GRAPHIC ORIGINALS AND CAPABLE OF PROVIDING PERMANENT REPRODUCTIONS STABLE AGAINST FURTHER HEATING, SAID COPY-SHEET PRODUCT INCLUDING A VISIBLY HEAT-SENSITIVE LAYER CONTAINING, IN INTIMATE ASSOCIATION, A NORMALLY SOLID CONDENSATION COMPOSITE OF A HETEROCYCLIC HYDRAZONE AND AN AMINE-REACTIVE ORGANIC COMPOUND, AND A PHOTOSENSITIVE N-HALO-SULFONANILIDE OXIDIZING AGENT SOLID AT TEMPERATURES BELOW ABOUT 55*C. AND WHICH IS RENDERED INACTIVE AS AN OXIDIZING AGENT BY EXPOSURE TO ACTINIC RADIATION; AND SAID LAYER INCLUDING AN AZO COUPLER COMPONENT. 